Total knee replacement (“TKR”) requires many surgical steps and intraoperative decisions for a successful outcome. One of the steps requires the prosthesis to be rotationally aligned with the epicondylar or flexion axis of the distal end of the femur. The epicondylar axis is generally believed to be externally rotated approximately three degrees with respect to the posterior condyles. However, this is only an approximation since the actual value varies from patient to patient. Additionally, it is very difficult to definitively identify the epicondylar axis because its origin, the insertion sites of the medial and lateral collateral ligaments, is not an exact point, but rather an area of attachment. Therefore, current TKR procedures approximate the epicondylar axis in a visual manner as opposed to actually measuring the position of the axis.
Except for computer-assisted navigated TKR, there currently exists no instrumented means of measuring the curvature of the condyles of a knee. The present invention relates to an apparatus used to measure the radius value of a curved surface of a knee as well as an improved method of determining the flexion axis of a knee.
Current non-computer assisted method of rotational alignment rely on the epicondylar axis or referencing of the posterior condyles. These instruments are either set at a fixed angle or adjustable. Whether fixed or adjustable, the surgeon has no idea what that specific patient's natural anatomic angle of external rotation is and will ultimately result in suboptimal placement of the component.